It is desirable to be able to quantify the amount of distortion of an image that is perceptible to a human. Such quantification provides a tool for designing imaging systems, image compression schemes, and imaging media. A designer can trade-off the cost of reducing image distortion with the degree of human perceptibility of that distortion.
Most algorithms for determining image distortion output a single numerical value that indicates an amount of distortion. While providing a single value simplifies the trade-off process, it does not indicate which portions of the image are distorted. In some instances, it may be desirable to increase distortions in some areas of an image while simultaneously decreasing distortions in other areas.
Further, many algorithms, especially those that provide a single value, do not distinguish between different types of distortion. For example, some algorithms cannot distinguish between a first image and a second image where the second image has less blur but more noise than the first image. The images are not the same, but the algorithms rate them the same.
There is a need for a method and apparatus which determine the visual differences between images and provide a visual indication of these differences.